Combustion and Emission Characteristics of an Ammonia-Hydrogen Engine under Passive- and Active-Jet Ignition 2024-01-2109
In the context of carbon neutrality, ammonia is considered a zero-carbon fuel with potential applications in the transportation sector. However, its high ignition energy, low flame speed, and high natural temperature, indicative of low reactivity, make it challenging to be applied as a sole fuel in engines. In such a scenario, the use of another zero-carbon and highly reactive fuel, hydrogen, becomes necessary to enhance the combustion of ammonia. Furthermore, jet ignition, a method known for improving engine combustion performance, may also hold potential for enhancing the combustion performance of ammonia engines. To explore the applicability of jet ignition in engines, this study conducted experimental research on a single-cylinder engine. Two ignition methods were employed: passive jet ignition of premixed ammonia-hydrogen at a compression ratio of 11.5, and active jet ignition of pure ammonia using hydrogen jet flame at a compression ratio of 17.3. Experimental results indicated that, under passive jet ignition conditions, as the proportion of ammonia energy increased, the engine's combustion phase was delayed, combustion duration was extended, and peak cylinder pressure and peak heat release rate decreased. Additionally, as the proportion of ammonia energy increased, the engine's NOx emissions decreased, while unburned ammonia emissions increased. The engine achieved the highest indicated thermal efficiency at an 80% ammonia blending ratio. Under active jet ignition conditions, the jet flame could stably ignite pure ammonia under lean conditions. However, under lean conditions, the low reactivity of pure ammonia led to prolonged combustion duration, reduced ammonia combustion efficiency, and a significant increase in unburned ammonia emissions, resulting in decreased thermal efficiency.
